In a wire electric discharge machining that uses water as a machining liquid, control of the conductivity of the machining liquid is essential to stably perform the machining. In order to control the conductivity of a machining liquid used for the wire electric discharge machining, a method of deionizing a machining liquid by using a water purifying resin is generally used.
However, an iron-based material is often used for work pieces, and when an iron-based metal such as die steel or tool steel is machined in a deionized machining liquid, the iron-based metal corrodes. Thus, there arises a problem that corrosion has an influence on the machining accuracy. For this reason, a method using anticorrosive ions has been known.
Patent literature 1 discloses a technology in which a column filled with an anticorrosive-ion exchange resin and a column filled with a water purifying resin are provided, and if the conductivity of a machining liquid is smaller than a predetermined value, all of the machining liquid flows into the column filled with the anticorrosive ion exchange resin; whereas if the conductivity of the machining liquid is larger than the predetermined value, some of the machining liquid flows into the column filled with the water purifying resin, and the remaining machining liquid flows into the column filled with the anticorrosive-ion exchange resin. Patent literature 2 discloses a technology in which a water purifying unit and an anticorrosive-ion generating unit are provided, similarly to patent literature 1, and when a value of a conductivity of a machining liquid is larger than a predetermined value, the machining liquid flows into the water purifying unit; whereas when the value of the conductivity is smaller than the predetermined value, the machining liquid flows into the anticorrosive-ion generating unit.